Multi-digit electrical door lock



March 6, 1962 E. J. LEONARD 3,024,452

MULTI-DIGIT ELECTRICAL DooR Loox Filed Aug. 22, 195e 2 sheets-sheet 1ATToR'N Evs EDWARD J. Laonmrz March 6, 1962 E. J. LEONARD 3,024,452

MULTI-DIGIT ELECTRICAL DOOR LOCK Filed Aug. 22, 1958 2 Sheets-Sheet 2FKa. 4

BIO

Y INVENTOR. o EDWARD J. LEONARD BY ifw, @644/74 @ad ATTORNEYS UnitedStates Patent f 3,024,452 MUL -DlGlT ELECTRHCAL DOOR LOCK Edward Ii.Leonard, Chicago, Ill., assigner to International Telephone andTelegraph Corporation, a corporation of Maryiand Filed Aug. 22, 1953,Ser. No. 756,591 Claims. (Cl. S40-274) This invention relates to amulti-digit electrical door lock. lts principal object is to provide arnulti-digit electrical door lock of great security against the doorbeing unlocked by anyone other than an authorized person who knows thecurrently-assigned multi-digit unlocking number.

lt is generally conceded that multi-digit combination locks are moresecure against being opened by 'unauthorized persons than are the usualkey-operated locks. The usual combination locks, however, are notentirely satisfactory where great security is important. Among otherreasons, changing the combination, as when it is suspected thatunauthorized persons may have learned the combination or when previouslyauthorized persons are no longer authorized, is usually a time-consumingoperation which often requires the services of a trained locksmith,wherefore the combination is frequently left unchanged too long.

Moreover, the ordinary combination lock may sometimes be opened onrepeated trials by unscrupulous persons who have become expert in such aprocedure.

According to the invention, the foregoing and other disadvantages ofprior devices are overcome by providing a multi-digit electrical doorlock so arranged that the cornbination may be changed readily from timeto time as desired by merely altering electrical connections, as byrotating each of a number of digit switches to respective positionscorresponding to the digits of the desired new combination.

Further, according to the invention, hunting for the combination bytrial digit transmission is thwarted, in that any attempt at digittransmission which fails to coincide with the currently assignedcombination establishes a locked condition which disables the lock fromopening and sounds an alarm, such locked condition being maintaineduntil cleared, as after an investigation has been made.

Conveniently, the digits of any desired combination assigna'ble to thelock are imparted to the control meche anisrn by a single set of digitkeys or pushbuttons which rnay be mounted outside the door controlled bythe lock. A feature of the disclosed circuit arrangement is that thelack of knowing the combination cannot be circumvented by opening thepushbutton set and effecting connections between the then exposedconductors connected thereto.

According to a further feature, the successive digits of the combinationmust be transmitted with no undue delay between digits, failing whichtiming interval elapses to cancel the portion of the combination alreadysent and to require a complete new sending of the combination. Thistiming feature is employed to limit the unlocked interval, therebybarring entry if the one seeking entrance delays opening the door formore than a predetermined comparatively short interval after having sentthe correct complete combination.

According to a further feature of the invention, an alarm is sounded ifthe door is held open for more than a predetermined interval, therebyguarding against an authorized person accidentally or otherwise leavingthe door open and unlocked to permit entry of unauthorized persons. Arelated feature is that the door-open alarm may be cut off when desired,as when apparatus or equipment is required to be moved through the doorover an 3,024,452 Patented Mar. e, 1962 ICC extended period, in whichcase a warning signal is given, at any desired location, that the areareached through the door is temporarily unguarded.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent, and theinvention itself will be best understood by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings, comprising FIGS. l to 4, wherein:

FIG. l is a general plan View of an application of the invention to anarea protected by a door having a combination door lock according to theinvention;

FIGS. 2 and 3 show in circuit diagram the electrical apparatus indicatedin FIG. 1; and

FIG. 4 shows a modification of the digit apparatus of FlG. 2.

FIG. l shows a plan diagrammatic view of the invention being applied toa door which gives access to a protected area PA. The door 100 isillustrated as being hinged to open inwardly into area PA and may beprovided with the usual illustrated turnable door knobs `for opening thedoor, the outside knob being understood t0 be ineffective unless theldoor lock DL is electrically actuated to permit the `door to be openedfrom the outside.

The principal controlling apparatus for the electrical door lock iscontained within the closed compartment 110, to which the door lock DLis connected by conductors 102. A set of pushbuttons PB is shown mountedon the wall outside of door 100, being the pushbuttons PB illustrated incircuit diagram in FIG. 2. Buttons PB are connected to apparatus byconductors 101. Alarm AL, connected to 110 by conductors 105 is providedto sound an alarm when the occasion arises, as when any unassignedcombination is used in an unauthorized attempt to unlock door 160.Release key RK, connected over conductors 104, may be employed torelease such an alarm condition. RK may be in a control area CA asindicated, or at such location as may be deemed best for any giveninstallation.

Door 100 is provided with door switch DS, connected to apparatus 110over conductors 103 to cause alarm AL to be operated if the door 100 isheld open longer than a predetermined timed interval. The door-openalarm condition may be disconnected at cut-off device CO when desired,in which case warning light WL is lighted, the circuit arrangement beingas shown in FIG. 3.

Pushbutton set PB of FIG. 1 is shown in circuit diagram in FIG. 2 as aset of ten pushbuttons, or equivalent automatically restoring switches 1to 9 and 0. Each pushbutton of set PB includes a pair of normally opencontact sets, closable upon actuation of the pushbutton. Each button isthus adapted to send either one element or two elements of a`four-element code employed for transmitting the ten digit valuescorresponding respectively to the buttons of set PB. Alternating currentdelivered from power conductor Pl, over conductor P in group 101, isrectified at the oppositely directed rectiiers 203 for delivery overposi-tive conductor 201 and negative conductor 262 to the pushbuttons,whence it may be applied (according to the button pushed) over either orboth `of the conductors T and R in group 101.

Four polarized code element relays CA to CD are provided withinapparatus -1r10 of FIG. l to respond singly or in combination accordingto which of the buttons 1 to 0 of set PB is actuated. Relays CA and CBare connected in series between conductor T and the return `alternatingcurrent conductor P2, while relays CC and CD are connected in seriesbetween conductor R and conductor P2. Relays CA and CC are positivelypolarized by their respective illustrated shunting rectiers, andconductors CB and CD are similarly negatively polarized, Wherefore anyrelay CA to CD responds only when current of the indicated polarity isdelivered over its associated circuit.

Digit relays DA to DD are controlled respectively by polarized relays CAto CD.

FIG. 2 also shows door lock DL of FIG. 1 in the form of a conventionalsolenoid, and it shows door switch DS of FIG. 1 in the form of anormally closed switch which opens upon door 100 being opened from itsillustrated closed and locked position, and remains open until the dooris again closed and locked.

FIG. 3 shows transformer 302 which receives energizing current fromsupply conductors 301 and supplies 50- volt `alternatingcurrent power toconductors P1 and P2. Rectiers 303 provide full-wave rectification fromconductors P1 and P2 to the positive and negative conductors 304extending to the illustrated direct-current apparatus. The positive oneof these conductors is shown grounded. Each connection of that conductoris indicated in the circuit diagram as a conventional ground symbol.Each connection of the negative one of the conductors 304 is indicatedin the circuit diagram by a terminal with the negative sign appliedthereto.

FlG. 3 further shows the digit assigning apparatus cornprising switchesDS1 to DS3 Whereat connections are made between selected digitconductors D (controlled by relays DA to DD of FIG. 1) and thedigit-receiving relay apparatus, to the right of the digit switches,according to any desired one of one thousand digit combinations.

The digit-receiving apparatus comprises digit-responding relays D1 andD2 which operate in combination with each other and with transfer relayTR to eifect unlocking of the door responsive to receipt of thecurrently assigned combination. Interval-timer relay IT times theintervals between successive digits, together with the unlock intervalfollowing the final digit of the combination, during which the door maybe opened. Guard relay G, controlled over guard conductor GC from FIG.2, controls alarm relay ALR to sound an alarm responsive to any digitnot conforming to the assigned combination. Doortimer relay DT isnormally held energized by door switch DS of FIGS. 1 and 2.

FIG. 3 also shows alarm device AL and release key RK of FIG. 1, alongwith cut-off key CO and warning light WL.

Selting the Combination With the system installed as shown, any desiredone of the one thousand three-digit combinations (111 to 000) accordingto which of the buttons in set PB may be operated to unlock the door100, is assigned at individually rotatable digit switches DS1 to DS3. Ifthe combination 3, 6, 1 is desired, the digit switches are individuallyrotated from such positions as they may occupy to the respectivepositions shown in FIG. 3. Then, switch DS1 is on its third terminal, incontact with wire 3 in digit group D; D52 is on its sixth terminal, incontact with wire 6 in group D; and switch DS3 is on its first terminal,in contact with wire 1 of group D. When a different combination isdesired, one, two or all three, of the switches DS1 to DS3 are merelymoved to accord with the respective digits of the desired newthree-digit combination.

Unlocking Operation With the door 100 of FIG. l in its normally'closedposition, an authorized person wishing admittance to protected `area PAneed only operate the pushbuttons PB in accordance with the respectivedigits of the currently assigned three-digit combination, which may beassumed to be the number 361, in accordance With the respective digitsof which digit switches DS1 to DS3 are illustrated as being positioned.For this purpose, buttons, 3, 6, and 1 of set PB are actuatedmomentarily, one at a time, in

the indicated succession to cause the solenoid of door lock DL to becomeenergized temporarily to unlock the door 100. Responsive to each ofthese pushbutton operations, the corresponding combination of coderelays CA to CD is operated in accordance with the code shown in thefollowing code table:

Code Table A B C D X X X X X X X X X X The relays P-A to PD correspondrespectively to the clements A to D in the above code table, and tneletter "X is used for each digit wherein any such code element appears.

It will be observed from the `above code table that the digits andcorresponding pushbuttons have assigned thereto the `following codecombinations respectively, considering the digits in their indicatedorder from l to 9 and 0: A, B, AB, C, AC, BC, D, AD, BD, and CD. It willbe understood, of course, that any desired other orders of assignment ofcode combinations may be employed in place of the one specically given.

First Digit When button 3 of group PB of FIG. 2 is actuated inaccordance with the first digit "3 in the currently assignedcombination, it connects each of the polarized con ductors 201 and 202to conductor T in group 101, thereby supplying effectively unrectifiedcurrent over conductor T and through relays CA and CB in series, to thereturn power conductor P2. Relay CA receives current on each positivehalf cycle over conductors P1 and P2, and relay CB receives current oneach negative half cycle. Relays PA and PB thus both operate at verynearly the same time, the initial current to one relay beingtime-displaced less than nine milliseconds from the initial current tothe other relay. During the time that either such relay is not receivingcurrent directly while the button remains pushed, a local circulatingcurrent continues therethrough by way of the shunting rectifier of therelay, as a consequence of which both relay PA and PB remain operatedcontinuously for as long a time as button 3 remains actuated.

Digit relays DA and DB both operate responsive to operation of theirrespectively associated relays PA and PB. Contacts 1 of relays DA and DBground guard conductor GC (in common with relays DA to DD, whenoperated), thereby closing a circuit through back contacts 1 of relaysD1 and D2 for guard relay G. Contacts 1 of relay G lock ground on guardconductor GC through contacts 2 of ALR, whereby relay G remains operatedindependent of relays DA to DD. Contacts 2 of relay G close a circuitfor alarm relay ALR to ground over conductors 104 and release key RK.Relay ALR is slowoperating and. consequently, has its circuitinterrupted by the hereinafter described operation of relay D1 and theconsequent release of relay G when (as currently assumed) the relays ofFIG. l have received a pushbutton setting in accordance with theassigned unlock combination.

Referring further to the noted operation of digit relays DA to DD, itwill be observed that ground applied to the apex of the illustratedcontact pyramid of these relays is normally maintained disconnected fromall of the ten wires 1 to 0 in digit group D by contacts of theserelays. With any one, or any combination, of the relays DA to DDoperated, the marking ground can be placed on no more than one of thewires 1 to (l of D. With relays DA and DB now operated as assumed,ground is applied to digit conductor 3 of group D, the grounding paththrough back contacts 2 and 3 of relays DD and DC, and front contacts 5and 7 of relays DB and DA, to conductor D3.

The ground thus placed on conductor 3 of group D traverses the brush ofthe rst digit switch DS1, thereby closing a circuit through backcontacts 5 and 3 of relays TR and D2 for the lower winding of digitrelay D1. Relay D1 thereupon operates. At its front contacts 2, itoperates interval-timer relay IT through back contacts 2 of relay D2, atthe same time discharging the normally charged timing condenser 305through resistor 166. Relay D1 is locked to ground through its own lowerwinding and the lower winding of D2, through front contacts i and 1 ofD1 and IT, and back contacts 3 of ALR, but no substantial current iiowsover this locking circuit as long as the initial circuit for relay D1remains established, over DS1. Back contacts 1 of relay D1 opencircuitand restore guard relay G, which open-circuits alarm relay ALR beforethat relay has had time to operate.

Relay D1 remains operated, and D2 remains restored, until the actuatedpushbutton (3 of set PB) is restored, whereupon relays CA and CBrestore, permitting relays DA and DB to restore. Conductor GC andconductor 1 of group D are thereby ungrounded. The initial circuit ofthe lower winding of relay D1 is thereby opened, leaving relay D1operated in its described locking circuit, in which circuit relay D2 nowoperates to mark the end of the transmission of the irst digit of thecombination. Back contacts 2 of D2 open the operate circuit ofintervaltimer relay IT, leaving that relay operated in the rechargecircuit of the now-discharged condenser 395, for a maximum interval ofperhaps five seconds, during which the correct second digit of thecombination must be received to prevent relay IT from restoring andclearing out the digit record. Front contact 1 of D2 again connects thewinding of relay G to conductor GC, through front contacts 1 of D1.Contacts 5 of D2 disconnect the brush of switch DS1, which has nowserved its purpose in receiving the first digit marking, and contacts 3of D2 connect the brush of D32 in circuit preparatory to the receipt ofthe second digit (6 in the illustrated example) of the currentlyassigned combination.

Second Digit When pushbutton 6 of set PB is actuated to send the seconddigit (6) of the assigned combination, it connects the positive andnegative half-cycle conductors 201 and 262 respectively to conductors Rand T of group 101. Negative polarized relay CB is responsively operatedover conductor T, and positive polarized relay CC is operated overconductor R, according to the code BC indicative of the digit 6. Digitrelays DB and DC responsively operate, grounding conductor GC toreoperate guard relay G, this time through front contacts 1 of DI, D2,with results as described. CB and CC also place ground on conductor 6 ofgroup D at their front contacts 4 and 3, the grounding path includingback contacts 2 and 5 of unoperated relays DD and DA. Ground on 6 ofgroup D closes a circuit through the second digit switch DS2, and thencethrough contacts 3 of D2 for the upper winding of D2, whereby D2 visheld operated during the remainder of the seconddigit transmission. Abranch path energizes the upper winding of relay DI, through contacts 1of TR and 3 of D1. Diterential relay D1 is thereby magneticallyneutralized and restored. Its previous locking circuit is opened at itsfront contacts 4 (leaving D2 dependent upon its upper winding), and theupper winding of D1 is disconnected at contacts 3 of D1. Thestill-operated interval-timer relay IT is reenergized, and condenser 305is again discharged, this time through back contacts 2 of D1 and frontcontacts 2 of D2. Guard relay G is again disconnected and restored, thistime at front contact 1 of D1.

Upon D1 restoring, with D2 held operated, transfer relay TR is nowoperated through contacts 4 of D1 and D2, its operating circuit furtherincluding contacts 1 and 3 of IT and ALR. At its contacts 2, TR locksoperated independent of contacts of D1 and D2, but with no otherimmediate result, since operation of TR contacts 1, 3, and i is merelypreparatory for the moment.

When transmission of the second digit is ended, by restoration of button6 of PB, relays CB and CC responsively restore, restoring DB and DC toagain unground conductors GC and D6. The circuit path through DS2 forholding the upper Winding of D2 is thereby opened, whereupon D2 restoresand disconnects from DSZ.

Relays D1 and D2 are now both again in restored condition, and transferrelay TR stands locked operated. The energizing circuit ofinterval-timer relay IT is again opened, this time at front contacts 2of D2 to set a time limit on the interval permitted between the secondand third digits of the combination. Moreover, guard relay G isreconnected at back contacts 1 of D1 and D2 preparatory to checking thecorrectness of the third digit, when received.

Third Digit When the third digit l is transmitted, by actuation ofpushbutton 1 of PB, current of positive polarity from 261 is transmittedover conductor T, opera-ting relay CA, which operates DA. GC is againgrounded, to operate relay G for the third time with results asdescribed. DA also grounds conductor 1 of D at its contacts S, by Way ofback contacts 5, 3, 2 of DB, DC, DD. A circuit is thereby closed throughthe brush of third digit switch DS3, and thence through front contacts 3of TR and back contacts 5 of D2, for reoperating D1 through its lowerwinding. Thereupon D1 again looks operated through its front contacts 4,as described; it reenergizes IT at its front contacts 2; and it againopen-circuits and restores G at its back contacts 1.

When transmission of Ithe third digit is ended, and relays CA and DAhave restored, the consequent ungrounding of digit conductor 1 of Dungrounds the brush of DS3 to open the operate circuit of D1. Thatrelay, however, again remains operated in its local locking circuit,wherein relay D2 again reoperates, again opening the energizing path ofrelay IT, this time to set a time limit on the unlocking intervalpermitted for opening the door 16)` of FIG. 1.

Now, for the first time during the operations being described, all threeof the digit-checking relays D1, D2, and TR stand operated at the sametime.

Unlocking and Clearing Ont Ground is now extended through contacts 5 ofrelay D1, by way of contacts 6 and 4 of D2 land TR, and over conductors102, to energize the solenoid of door lock DL, whereby the door (160 ofFIG. l) looked by DL is unlocked during the interval that DL isenergized. During that interval, of perhaps five seconds, door may beopened.

During the interval that relays D1, D2, and TR are all operated and heldoperated through front contacts 1 of IT, no further digit transmissionfrom PB can be effective over digit conductors D- and switches DS1 toDS3. DS1 and DS3 are disconnected at contacts 5 of D2 and DSZ isdisconnected from D1 at contacts 1 of D1. The existing connection of D52to the upper winding of D2, at 3 of D2, is immaterial because D2 isalready operated.

When the described unlocking circuit over conductors lil-2 has beenclosed for about live seconds, intervaltimer relay IT restoresresponsive to condenser 305` becoming recharged therethrough. ITopen-circuits and 7 restores relays D1, D2, and TR, returning thecombination-recording apparatus to normal and opening the describedcircuit over conductors 102 for door lock DL. If the door (100 of FIG.l) is still in closed position, it immediately relocks. Otherwise, itrelocks upon being closed.

Door-Open Alarm When the door 100 is open, either for entry to or exitfrom `the protected area, door switch DS of FIGS. l and 2 opens, therebyopening the normally closed circuit over conductors 103 for door-timerrelay DT. Relay DT is shunted by condenser 307 in series with limitingresistor 308. It is maintained operated in the discharge path of 307 fora selected interval, such as ten seconds, long enough for an authorizedperson (or a small group) to pass through the door. Usually, the openeddoor is thereafter reclosed to reenergize DT before DT has had time torestore. However, if the door is left open beyond the short intervalpermitted, relay DT restores when condenser 307 has effectivelydischarged therethrough. Thereupon, it closes a circuit through itscontacts 1, and closed contacts of CO, over 105 for the alarm bell AL,thereby sounding an alarm. Such alarm continues to sound until the dooris reclosed, whereupon relay D1 is reenergized over conductors 103 toopen the alarm circuit.

If the door is required to be held open for longer than the timinginterval, as for the entry of furniture or equipment, for example, thedoor-controlled circuit of alarm AL may be opened by operation of key orswitch CO, which disconnects the door-open alarm circuit and lightswarning light WL as a signal that the door-open alarm is disconnected.

Sending-Gap Clearozlt If, at any time during the sending of the digitsof the currently assigned three-digit combination, the sender neglectsto push the button for the next digit for more than the five seconds orso that IT will remain operated in the described recharging circuit ofcondenser 305, relay IT restores and releases any operated ones of digitrecording relays D1, D2, and TR. The apparatus is thereby cleared out inreadiness for a new code transmission.

Wrong-Combination Alarm When the wrong digit combination is transmittedfrom PB, which is any combination differing in one or more digits fromthe combination currently assigned at switches DS1, DS2, DS3, alarmrelay ALR is operated responsive to the first transmitted digit (first,second, or third) which differs from the corresponding digit of theassigned com bination. It has been described that guard relay G isoperated over guard conductorGC and locked each time any one of therelays DA to DD responds to a digit sent from a button of set PB. It hasbeen further described that relay G is almost immediately disconnectedand restored by relay D1 for each received digit of the assignedcombination, before slow-operating relay ALR has had time to operate.For example, the described operation of relay D1 on the first digit andagain on the third digit, disconnects relay G at back contacts 1 of D1,relay D2 than being in restored condition. The described disconnectionof G on the second digit (with relay D2 being held operated) occurs atfront contacts 2 of D1 on the forced release of D1.

When any transmitted digit (either the first, second, or third) fails tobe the corresponding digit of the assigned combination, the currentlyconnected one of the digit switches DS1 to `DS3 then fails to carrycurrent to the concerned winding (lower or upper) of D1, wherefore D1fails to respond, leaving relay G operated over GC. The circuit of ALRthus remains closed over conductors 104 and through contacts 2 of relayG for a sufhcient interval (such as twenty-five milliseconds) forslowoperating relay ALR to operate. Upon operating, relay ALR locksoperated at its contacts 2 independent of contacts 2 of relay G.Contacts 1 of ALR open the locking circuit of G. At its back contacts 3,relay ALR clears out all operated ones of relays D1, D2, and TR,restoring IT and relay G, unless a button of PB is being held operated.Front contacts 3 of relay ALR energize alarm AL over conductors 105,thereby sounding an alarm.

When the alarm condition has been suitably investigated, release switchor key RK is temporarily actuated, open-circuiting and restoring ALR,which unlocks at its contacts 2 and opens the alarm circuit at its frontcontacts 3, thereby terminating the alarm condition.

Nullfcaton 0f Hunting Attempts Attempts at hunting for any one of thethree digits of the currently assigned combination by actuating two ormore of the ten pushbuttons of set PB, together or in succession, arenullified in the disclosed arrangement, wherein (l) the seriesarrangement Within the contact pyramid of relays DA to DD insures thatno more than one of the ten digit conductors 1 to 0 of group B can beenergized at the same time, irrespective of the num ber of pushbuttonsactuated; and (2) self-locking guard relay G, which controls alarm relayALR, locks operated on any digit transmission until relay D1 acts(operates on first and third digits and restores on the second), to thusoperate the self-locking alarm relay ALR at the end of an interval tooshort to permit the effective actuation of a second one of thepushbuttons without relay ALR operating to lock at its contacts 2. Theoperation of ALR cancels any recorded information at its back contacts 1and 3, and energizes alarm circuit 105 at its front contacts 3, asdescribed.

For example, if relay G requires ten milliseconds to operate, and ifrelay D1 is so wound and adjusted that it requires a circuit closure ofits lower winding for at least twenty milliseconds for its operationthrough switch DS1 or DS3, and a like interval of circuit-closure of itsupper winding through switch D52 for its restoration, then twosuccessive effective pushbutton operations of a hunting attempt mustrequire a minimum of forty milliseconds of circuit closure, whichexceeds the thirty-five milliseconds of effective circuit closure (tenfor G, and twenty-five for ALR) required for relays G and ALR to operatesuccessively and lock if the first effective button pushed does notcoincide with the assigned combination to cause relay D2 to respond.

Referring to FIG. 4, the modification therein includes ten pushbuttonsB1 to B10 (only B1, B2, and B10 being shown), which replace set PB ofFIGS. l and 2, and render relays CA to CD and DA to DD unnecessary.These buttons are connected to the control apparatus by the elevenconductors 401, comprising a ground-supply conductor and ten digitconductors 1 to 0 which comprise the conductors in set D3, correspondingto set D, of FIGS. 1 and 2.

When any digit button B1 to B10 of FIG. 4 is actuated, it grounds theassociated digit conductor in group D of FIG. 3, at the same timegrounding guard conductor GC of FIG. 3 by way of the associated one ofthe diode rectifiers R1 to R10.

It will be observed that actuation of two or more buttons B1 to B10results in ground being placed on only one digit conductor, since theground supply is chained through back contacts of the buttons.

The modification of FIG. 4 has the economical advantage over FIG. 2 innot requiring the eight relays CA to CD and DA to DD, which is partlyoffset by requiring additional conductors in connecting group 401. Thisadvantage is usually outweighed by the fact that an unauthorized personmay succeed in forcing access to the wiring of the pushbutton set ofFIG. 4 and thus, for example, strap together all ten digit conductors,to cause the grounding of one of them to constitute grounding all ofthem, thereby effectively closing a circuit through any currentlyconnected switch DS1 to DS3 irrespective of its setting. It is clearthat no such lack of security exists in the arrangement of FIG. 2,wherein the disclosed contact pyramid of relays DA to DD', notaccessible from outside the protected area, is arrranged as described topreclude the grounding of more than one digit conductor at a time.

While I have described above the principles of my invention inconnection with specic apparatus, it is to be clearly understood thatthis description is made only by Way of example and not as a limitationto the scope of my invention.

I claim:

l. A system for unlocking a lockable door, comprising an energizableunlocker, a group of digit pushbuttons and digit conductorscorresponding respectively thereto, means responsive to the pushing ofany pushbutton for energizing the corresponding digit conductor, aseries of code conductors, code-assigning means for connecting any codeconductor to any desired digit conductor for energization thereover,including means for connecting more than one code conductor to the samedigit conductor, a sequence device with which the code conductors areassociated and to which the iirst code conductor is normally connected,with the remaining code conductors being normally disconnectedtherefrom, means responsive to the energization of any code conductorpreceding the last for operating the sequence device to disconnect thecurrently connected code conductor from the sequence device and toconnect the next succeeding one thereto, and means responsive to theenergization of the last code conductor when connected to the sequencedevice for operating the sequence device to energize the said unlocker.

2. A system for unlocking a lockable door, comprising an energizableunlocker, a group of digit pushbuttons and digit conductorscorresponding respectively thereto, means responsive to the pushing ofany pushbutton for energizing the corresponding digit conductor, aseries of code conducto-rs, code-assigning means for connecting any codeconductor to any desired digit conductor for energization thereover, asequence device with which the code conductors are associated and towhich the rst code conductor is normally connected with the remainingcode conductors being normally disconnected therefrom, means responsiveto the energization of any code conductor preceding the last foroperating the sequence device t disconnect the currently connected codeconductor from the sequence device and to connect the next succeedingone thereto, and means responsive to the energization of the last codeconductor when connected to the sequence device for operating thesequence device to energize the said unlocker, the said means forenergizing the said digit conductors including means for preventing theenergization of more than one digit conductor responsive to the pushingconcurrently of more than one pushbutton.

3. A system for unlocking a lockable door, comprising an encrgizableunlocker, a group of digit pushbuttons and digit conductorscorresponding respectively thereto, means responsive to the pushing ofany pushbutton for energizing the corresponding digit conductor, aseries of code conductors, code-assigning means for connecting any codeconductor to any desired digit conductor for energization thereover, asequence device with which the code conductors are associated and towhich the first code conductor is normally connected with the remainingcode conductors being normally disconnected therefrom, means responsiveto the energization of any code conductor preceding the last foroperating the sequence device to disconnect the currently connected codeconductor from the sequence device and to connect the next succeedingone thereto, means responsive to the energization of the last codeconductor when connected to the sequence device for operating thesequence device to energize the said unlocker, the said pushbuttonsbeing remote from the said means for energizing the digit conductors, acontrol line extending from the pushbuttons to the last said means andcomprising line conductors fewer in number than the digit conductors,the said means responsive to the pushing of the pushbuttons comprisingmeans for imparting to the line conductors a separate distinctive codefor each button pushed, and the said means for energizing the digitconductors further comprising means for energizing a separate digitconductor for each said distinctive code applied to the line conductors.

4. A system for unlocking a lockable door, comprising an energizableunlocker, a group of digit pushbuttons and digit conductorscorresponding respectively thereto, means responsive to the pushing ofany pushbutton for energizing the corresponding digit conductor, aseries of code conductors, code-assigning means for connecting any codeconductor to any desired digit conductor for energization thereover, asequence device with which the code conductors are associated and towhich the first code conductor is normally connected with the remainingcode conductors being normally disconnected therefrom, means responsiveto the energization of any code conductor preceding the last foroperating the sequence device to disconnect the currently connected codeconductor from the sequence device and to connect the next succeedingone thereto, means responsive to the energization of the last codeconductor when connected to the sequence device for operating thesequence device to energize the said unlecker, a timing deviceresponsive to the said energization of any said code conductor forclearing out the sequence device at the end of a predetermined intervalthereafter, and reset means responsive to the energization ot' any codeconductor which is currently connected to the sequence device forresetting the timing device to restart the said interval.

5. A system according to claim 4, wherein the said clearing out of thesaid sequence device, by the restarted timing device at the end of thesaid interval following the energization of the said unlocker,deenergizes the unlocker.

6. A system for unlocking a lockable door, comprising an energizableunlocker, a group of digit pushbuttons and digit conductorscorresponding respectively thereto, means responsive to the pushing ofany pushbutton for energizing the corresponding digit conductor, aseries of code conductors, code-assigning means for connecting any codeconductor to any desired digit conductor for energization thereover, asequence device with which the code conductors are associated and towhich the rst code conductor is normally connected with the remainingcode conductors being normally disconnected therefrom, means responsiveto the energization of any code conductor preceding the last foroperating the sequence device to disconnect the currently connected codeconductor from the sequence device and to connect the next succeedingone thereto, means responsive to the energization of the last codeconductor when connected to the sequence device for operating thesequence device to energize the said unlocker, a timing device forestablishing a predetermined interval, and means controlled by thetiming device responsive to the elapse of said interval following thepushing of any said button, with no further button push intervening, forclearing out the sequence means.

7. A system for unlocking a lockable door, comprising an energizableunlocker, a group of digit conductors and means for momentarilyenergizing any desired one thereof while preventing the concurrentenergization of any other digit conductor, a series of code conductors,codeassigning means for connecting any code conductor to any desireddigit conductor for energization thereover, a sequence device with whichthe code conductors are associated and to which the rst code conductoris normally connected, with the remaining code conductors being normallydisconnected therefrom, means responsive to the energization of any codeconductor preceding the last for operating the sequence device todisconnect the currently connected code conductor from the sequencedevice and to connect the next succeeding one thereto, means responsiveto the energization of the last code conductor when connected to thesequence device for operating the sequence device to energize the saidunlocker, a guard conductor and means for energizing it concurrentlywith the said energization of any digit conductor, a guard relayoperable over the guard conductor responsive to energization thereof, analarm device responsive to the operation of the guard relay, and meansin the said sequence device for disconnecting the guard relay from theguard conductor to restore the guard relay, subject to the energizeddigit conductor being the one which is currently connected to thesequence device.

8. A system for unlocking a lockable door, comprising an energizableunlocker, a group of digit conductors and means for momentarilyenergizing any desired one thereof while preventing the concurrentenergization of any other digit conductors, a series of code conductors,code-assigning means for connecting any code conductor to any desireddigit conductor for energization thereover, a sequence device with whichthe code conductors are associated and to which the rst code conductoris normally connected, with the remaining code conductors being normallydisconnected therefrom, means responsive to the energization of any codeconductor preceding the last for operating the sequence device todisconnect the currently connected code conductor from the sequencedevice and to connect the next succeeding one thereto, means responsiveto the energization of the last code conductor when connected to thesequence device for operating the sequence device to energize the saidunlocker, a guard conductor and means for energizing it concurrentlywith the said energization of any digit conductor, a guard relayoperable over the guard conductor responsive to energization thereof,self-locking contacts operable by the guard relay to maintain the guardconductor energized as long as the guard relay is operated, an alarmdevice responsive to the operation of the guard relay, and means in thesaid sequence device for disconnecting the guard relay from theguardconductor to restore the guard relay, subject to the energizeddigit conductor being the one which is currently connected to thesequence device.

9. A system for unlocking a lockable door, comprising an energizableunlocker, a group of digit conductors and means for momentarilyenergizing any desired one thereof while preventing the concurrentenergization of any other digit conductors, a series of code conductors,codeassigning means for connecting any code conductor to any desireddigit conductor for energization thereover, a sequence device with whichthe code conductors are associated and to which the rst code conductoris normally connected, with the remaining code conductors being normallydisconnected therefrom, means responsive to the energization of any codeconductor preceding the last for operating the sequence device todisconnect the currently connected code conductor from the sequencedevice and to connect the next succeeding one thereto, means responsiveto the energization of the last code conductor when connected to thesequence device for operating the sequence device to energize the saidunlocker, a guard conductor and means for energizing it concurrentlywith the said energization of any digit conductor, a guard relayoperable over the guard conductor responsive to energization thereof,self-locking contacts operable by the guard relay to maintain the guardconductor energized as long as the guard relay is operated, means in thesaid sequence device for disconnecting the guard relay from the guardAconductor to restore the guard relay, subject to the energized digitconductor being the one which is currently connected to the sequencedevice, a slow-operating alarm device operable responsive to arelatively prolonged operation of the guard relay, and means responsiveto an operation of the alarm device for precluding energization of theunlocker and for sounding an alarm.

10. A system for unlocking a' lockable door, comprising an energizableunlocker, a group of digit conductors and means for momentarilyenergizing any desired one thereof while preventing the concurrentenergization of any other digit conductors, a series of code conductors,code-assigning means for connecting any code conductor lto any desireddigit conductor for energization thereover,

a sequence device with which the code conductors are as sociated and towhich the first code conductor is normally connected, with the remainingcode conductors being normally disconnected therefrom, means responsiveto the energization of any code conductor preceding the last foroperating the sequence device to disconnect the currently connected codeconductor from the sequence device and to connect the next succeedingone thereto, means responsive to the energization of the last codeconductor when connected to the sequence device for operating thesequence device to energize the said unlocker, a guard conductor andmeans for energizing it concurrently with the said energization of anydigit conductor, a guard relay operable over the gniard conductorresponsive to energization thereof, selflocking contacts on the guardrelay to maintain the guard conductor energized independent of its tirstsaid energizing means, means in the said sequence device fordisconnecting the guard relay from the guard conductor to restore theguard relay, subject to the energized digit conductor being the onewhich is currently connected to the sequence device, over the currentlyconneeted one of the said code conductors, a slow-operating alarm relay,contacts on the guard relay for operating the alarm relay subject to theguard relay remaining operated longer than a given minimum interval, andalarm-sounding means controlled by the alarm relay.

References Cited in the file of this patent UNITED STATES PATENTS1,685,329 Lynch Sept. 25, 1928 1,923,968 Chase Aug. 22, 1933 2,250,828Foss July 29, 1941 2,424,243 Lowell July 22, 1947 2,436,809 Joel Mar. 2,1948 2,563,127 McGoin Aug. 7, 1951 2,855,588 Allen Oct. 7, 1958 FOREIGNPATENTS 197,503 Great Britain May 17, 1923 OTHER REFERENCES Radio andTelevision News, April 1955, pp. 52, 53, 158, 159, L. Garner, Jr.

